linux-kernel - Re: [Freedreno] [PATCH] drm/msm/dpu: add DSC range checking during resource reservation

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Message-ID: <83fb974f-2c5a-0792-30f7-a317813f0eed@linaro.org>
Date:   Wed, 12 Apr 2023 21:56:44 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        freedreno@...ts.freedesktop.org, quic_sbillaka@...cinc.com,
        airlied@...il.com, andersson@...nel.org, robdclark@...il.com,
        dri-devel@...ts.freedesktop.org, dianders@...omium.org,
        vkoul@...nel.org, agross@...nel.org, daniel@...ll.ch,
        linux-arm-msm@...r.kernel.org, swboyd@...omium.org,
        sean@...rly.run, linux-kernel@...r.kernel.org
Subject: Re: [Freedreno] [PATCH] drm/msm/dpu: add DSC range checking during
 resource reservation

On 12/04/2023 21:50, Marijn Suijten wrote:
> On 2023-04-12 10:48:18, Abhinav Kumar wrote:
> [..]
>>> The only way to trigger this newly introduced range check is by omitting
>>> the DSC_x constants and manually writing e.g. an out-of-range value 10
>>> here, or setting DSC_NONE.  This is only allowed for interfaces.
>>>
>>
>> Correct, its just working on an implicit understanding that the indices
>> in the catalog
> 
> .. this sentence appears to be incomplete: what did you want to say? ..
> 
>> which might still be right stick to the RM limits.
>>
>> Thats why this is not bad to have.
> 
> What do you mean by "RM limits"?  We have constants in the kernel that
> both define the maximum number of blocks in these arrays and a
> predefined set of ids that block can have.  These are all used in
> constant structs in the catalog, so there's nothing "software" or
> SoC-specific limiting about this (except what is available in the
> arrays).
> 
> [..]
>> I think kuogee just added this to keep it consistent with other checks
>> present in the RM. So I didnt see any harm with that.
> 
> Yep, that's the only reason
> 
>> If he did see an issue, i will let him report that here.
> 
> If so an out-of-bounds constant was hardcoded in dpu_hw_catalog.c.
> 
>> Otherwise, I dont want to spend more time discussing this bounds check
>> when other blocks already have it.
> 
> I'll whip up a patch to clear out the extraneous lookup (assuming there
> is no other reason/dependency for it to be there...) and can follow that
> up with removing these range checks of known-good values in `const
> struct` fields.

Yes, please.

> 
> - Marijn

-- 
With best wishes
Dmitry